People at work had issues with the Windows 10 upgrade after upgrading from Windows 8.1 Update. This guy’s Surface Pro 3 Windows 10 display and keyboard wasn’t working properly especially when plugging in an external monitor, the Display Port didn’t work at all. Also when running Windows Update he was getting error code 0x80248007 when using Windows Updates.
Only way to fix this was to re-build from scratch, a nice clean install of Windows 10 and it doesn’t take long.
Download a full version of Windows 10 here https://www.microsoft.com/en-us/software-download/windows10 you need at least 3GB on a USB key, this tool will write the full Windows 10 install media to a USB key and makes it bootable. You can do this on any device.
Then boot up/start up the Surface Pro from the USB key as per this article http://www.microsoft.com/surface/en-au/support/storage-files-and-folders/boot-surface-from-usb-recovery-device?os=windows-10
As for activation, as Windows 10 activation is now tied to the device, as Windows 10 was already installed and activated previously, activation works seamlessly in the background.